Problems with diseased and arthritic hip joints have been with the human race for many years. Since early in the present century, various proposals and operative techniques have been proposed for partial or complete replacement of the hip joint. Some of the initial efforts at total hip replacement involved materials problems. Other of the more recently popular proposals for total hip joint replacement have involved the removal of substantial amounts of bone, either from the upper end of the femur, (the large upper leg bone), or from the hip socket or both. One of the more widely used techniques has involved the removal of the upper end of the femur and the use of a metal ball, somewhat smaller than the original ball at the upper end of the femur, mounted on a long pointed metal stem which was forced into the upper end of the femur with the pointed stem extending down and being secured in the intramedullary canal.
Incidentally, relative to the structure of the femur it has a dense "cortical" outer surface or shell, a porous "cancellous" structure just within the outer shell, and the central "intramedullary canal" in which the bone marrow and blood vessels, for example, are located.
Unfortunately, significant problems have been encountered with a number of prior total hip joint replacement techniques. More specifically, with regard to the femoral replacements of the metal stem type mentioned above, a number of cases of loosening and/or of breaking of the metallic ball-and-stem member have been encountered. Not only does a loosened or fractured stem create pain and hence lack of function but also the bone destruction created by the removal of the broken components constitutes a considerable problem for any future hip-joint salvage. In general it is believed that the excess amount of bone removal which has occurred in many prior operative techniques for hip joint replacement has been responsible for a higher incidence of medical problems than might otherwise be encountered.
In addition, it may be noted that it has previously been proposed to locate the socket in the plastic member which is secured in the hip, below center, to provide increased strength in the upper portion of tghe plastic socket member.
A principal object of the present invention is to provide a total hip joint replacement technique and structure which will involve a minimum removal of bone from the ball at the upper end of the femur and insure the fit of the plastic liner within the acetabular bone, or hip socket. A further object of the present invention is to maintain substantially the same diameter of ball and socket in the replacement, as was present in the original ball and socket of the patient. In this way more natural and more complete movement of the joint may be achieved and the customary "dead-space" normally created by conventional stem-type hip replacements is eliminated.